Prior art photosensitive protective films for semiconductor devices and dielectric films for multilayer printed boards utilize photosensitive polyimide, epoxy and silicone resins. For example, the photosensitive polyimide materials include those materials derived from polyamic acid as a polyimide precursor, typically those derived from polyamic acid by incorporating photosensitive radicals into carboxyl radicals thereon via ester bonds, as described in JP-A 49-115541 and JP-A 55-45746, and compositions comprising a polyamic acid and an amine compound having a photosensitive radical, as described in JP-A 54-145794. In these approaches, after a patterned coating is formed, imidization treatment must be effected at high temperatures above 300° C. in order to produce the desired polyimide film. This gives rise to the problems that the underlying substrate is limited by the requirement to withstand high temperatures, and interconnecting copper can be oxidized.
One solution to these problems is found in JP-A 10-274850, JP-A 10-265571, and JP-A 13-335619, which describe photosensitive polyimide materials comprising solvent-soluble resins which have been imidized, for the purpose of lowering the post-curing temperature. Since the resins in these patents are rendered photosensitive by incorporating (meth)acrylic radicals, they are susceptible to oxygen interference due to their photo-curing mechanism and also susceptible to film slimming during development. It is thus difficult to improve resolution. These materials do not meet all of the required properties.
Also proposed are positive compositions comprising a polyimide structure having phenolic hydroxyl radicals (JP-A 3-209478) or a polyamide structure (JP-B 1-46862 and JP-A 11-65107), combined with diazonaphthoquinone. These compositions suffer from the issues that their light transmittance makes it difficult to form thick films in excess of 10 microns and that the resin exerts little of its inherent curing characteristics because the resin must have a reduced molecular weight in order to ensure effective development and the amount of diazonaphthoquinone added as a sensitizer is large relative to the resin.
JP-A 2002-293877 discloses a photosensitive epoxy composition based on the reaction product of an epoxy compound with an unsaturated radical-containing carboxylic acid. The material derived from the epoxy compound can be cured at relatively low temperatures below 200° C., but the cured coating lacks flexibility and moisture-resistant adhesion and cannot be used in the application where high reliability is required.
Another known photosensitive material useful for the protection of substrates and circuits is a photosensitive silicone composition described in U.S. Pat. No. 6,590,010 or JP-A 2002-88158. The composition is curable at low temperatures below 250° C. and forms a film having reliability as typified by moisture-resistant adhesion, but has some drawbacks including insufficient chemical resistance to photoresist strippers having a high dissolving power such as N-methyl-2-pyrrolidone.